A portable wireless device, e.g. a cellphone, a wrist watch, etc. with built-in RF connectivity, contains and utilizes an antenna for wireless communication (transmit and receive). Some applications require more than one antenna. For example, wireless telecommunication operators have offered several generations of communication standards and different frequency bands. In such a case, at least two antennas tuned to at least two different frequency bands has been required to guarantee coverage over medium and longer distances. A changing dielectric environment exposes the antennas to frequency and impedance detuning. As a consequence, electric field antennas are not well-suited for such applications. However, magnetic loop antennas have low sensitivity to such dielectric changes.
FIGS. 1, 2, 3 and 4 show different configurations where a single feed drives two independent magnetic loop antennas. In FIG. 1, a single feed 100 feeds separate and distinct magnetic loop antennas 102 and 104 through separate inductive loops 106 and 108 connected in parallel. In FIG. 2, the single feed 100 feeds the magnetic loop antennas 102 and 104 through the separate inductive loops 106 and 108 connected in series. In FIG. 3, the single feed 100 feeds the magnetic loop antennas 102 and 104 through separate electrically conductive paths 302 and 304 connected in parallel. In FIG. 4, the single feed 100 feeds the magnetic loop antennas 102 and 104 through an electrically conductive path 402 in series.
Small portable wireless devices, such as wrist watch, have a limited amount of space for the components such as the antenna. Unfortunately, dual antenna configurations such as those shown in FIGS. 1-4 consume more space with the additional antenna and feed line relative to a single antenna configuration. Furthermore, the additional antenna and feed line increase overall cost and complexity of the device.